Conditions suitable for preparative isolation, quantitative separation and determination of plastochromanol-8 (PC-8), and their mild oxidation products were elaborated. Mild oxidation of PC-8 alone and with gammatocopherol (gamma-T) equimolare mixture by benzoquinone gives four and two new products, respectively. These products give Emmerie-Engel reaction. Four of gamma-T, three of PC-8 and two mixed mild oxidation products were found in linseed (Lea number = 49). It was also found that PC-8 derived from plant oils was a natural antioxidant better inhibiting autoxidation than alpha-tocopherol in the model system in which lard was the substrate.